German Patent Publication DE 41 11 405 C2 discloses a drive for the sley of a loom by means of bellcrank levers which are movable by an eccentric cam drive disk. One end of the bellcranks is journalled to the sley and the other end is journalled to the loom frame. This type of conventional bellcrank drive is intended to achieve a high operational speed even in large looms while still providing a sufficient time duration for the rest position of the sley for proper weft insertion.
The disclosure of the just mentioned German Patent Publication achieves this purpose in that the shaft that drives the cam disk is driven by a drive motor which is controllable in its r.p.m. in such a way that the shaft rotates at a higher r.p.m. when the sley is to be moved from its beat-up position along the beat-up line of the fabric into the retracted rear position and also when the sley is moved from the rear position to the beat-up position. By accelerating the sley motions in both directions the time duration for the rest position of the sley and reed is extended when the sley is stationary due to the configuration of the cam disk, the drive shaft rotates at a lower r.p.m. namely in the range of rotation when the sley is at rest.
According to the above conventional sley movement control it is important that the shaft which drives the cam disk is controllable in its r.p.m. by controlling the shaft drive motor.
It is further important that the time duration for the forward and backward move of the sley can be shortened by the higher drive r.p.m. to thereby provide the required extended rest time duration for the sley and reed.
Such a motion sequence of the sley, namely fast stop fast, is detrimental to the weaving of so-called pile fabric or terry cloth because a uniform pile formation is adversely affected by such motion sequence. This is so because a fast moving reed which is connected to the sley, necessarily cannot on its way to the beat-up line entrain the weft thread or a group of weft threads in a gentle manner. As a result of the relatively high speed of the reed during its beat-up motion toward the beat-up line the pile warp threads that must be formed into loops are at least partially pulled out of the weft thread group, whereby the resulting loops or piles have different lengths. If such a fabric is subsequently passed through a shearing operation, the loops or piles of smaller lengths are not cut by the shearing knives so that the appearance of the fabric is non-uniform. In other words, the terry cloth has a non-uniform appearance.
Another undesirable result of the high speed entrainment of the weft threads or weft thread groups by the reed is seen in that breaking of the warp threads and/or of the weft threads occurs frequently particularly of the base warp threads as well as of the pile warp threads.